Process for Making Composite Polymer

ABSTRACT

The method of making a pellet comprising wood pulp fiber and thermoplastic polymer, comprising extruding an extrudate comprising 10 to 50 weight % wood pulp fiber and 45 to 85 weight % thermoplastic polymer through a die, cutting a pellet from the extrudate, removing the pellet from the extrudate with water having a temperature less than the extrudate, filtering the pellet from the water. In one embodiment the wood pulp fiber in the pellet has a moisture content of 1% or less. In one embodiment the wood fiber does not swell.

FIELD OF THE INVENTION

The present invention relates to polymeric composites that are derivedfrom melt processing a polymeric matrix with chemical wood pulp fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are diagrams of a particle used to manufacture the polymericcomposite

FIG. 6 is a diagram of a mixer.

FIGS. 7 and 8 are diagrams of a pellet mill.

FIG. 9 is a diagram of a single screw extruder useful for manufacturingthe present pellet.

FIG. 10 is a diagram of an embodiment of apparatus and process formanufacturing a polymeric composite having a chemical wood pulp fibercontent of 50 weight % or less.

FIG. 11 is a cross-sectional view of the open face of the first twinscrew mixer.

FIG. 12 is a side view of the restrictor for the first twin screw mixer.

FIG. 13 is a front view of the restrictor for the first twin screwmixer.

FIG. 14 is a diagram of another embodiment of apparatus and process formanufacturing a polymeric composite having a chemical wood pulp fibercontent of 50 weight % or less.

FIG. 15 is a diagram of an underwater pelletizing system.

DETAILED DESCRIPTION

The present invention is directed toward providing an economical meansof producing composite polymeric materials which comprise wood pulpfiber and thermoplastic polymer. In an embodiment the wood pulp fiber isa chemical wood pulp fiber. In an embodiment the wood pulp fiber is akraft chemical wood pulp fiber. In an embodiment the wood pulp fiber isa bleached wood pulp fiber. In an embodiment the wood pulp fiber is ableached chemical wood pulp fiber. For simplicity the term “wood pulpfiber” will be used but it should be noted that bleached chemical woodpulp fiber has attributes not possessed by some of the other fibers.

The present invention can utilize a number of tree species as the sourceof the pulp fibers. Coniferous and broadleaf species and mixture ofthese can be used. These are also known as softwoods and hardwoods.Typical softwood species are various spruces (e.g., Sitka Spruce), fir(Douglas fir), various hemlocks (Western hemlock), tamarack, larch,various pines (Southern pine, White pine, and Caribbean pine), cypressand redwood or mixtures of same. Typical hardwood species are ash,aspen, cottonwood, basswood, birch, beech, chestnut, gum, elm,eucalyptus, maple oak, poplar, and sycamore or mixtures thereof.

The use of softwood or hardwood species may depend in part on the fiberlength desired. Hardwood or broadleaf species have a fiber length of 1-2mm. Softwood or coniferous species have a fiber length of 3.5 to 7 mm.Douglas fir, grand fir, western hemlock, western larch, and southernpine have fiber lengths in the 4 to 6 mm range. Pulping and bleachingand dicing may reduce the average length because of fiber breakage.

Cellulose wood pulp fibers differ from wood fibers because the ligninhas been removed and some of the hemicellulose has been removed. Thesematerials stay in wood fibers. The amount of material remaining in awood pulp fiber will depend upon the process of making it.

In a mechanical pulp the fibers are separated by mechanical means, suchas grinding, and the process may include steaming and some pre-chemicaltreatment with sodium sulfite. The lignin is softened to allow thefibers to part. Much of the lignin and hemicellulose as well as thecellulose remains with the fiber. The yield, the percentage of materialremaining after pulping, is high. The fiber can be bleached withperoxide but this process does not remove much of the material.

In chemical pulping, the lignin is removed during a chemical reactionbetween the wood chips and the pulping chemical. Hemicelluloses may alsobe removed during the reaction. The amount of material being removedwill depend upon the chemicals being used in the pulping process. Thekraft or sulfate process removes less material than the sulfite processor the kraft process with a prehydrolysis stage. The yield is higher inthe kraft process than in the sulfite process or kraft withprehydrolysis. The latter two process have a product with a highpercentage of cellulose and little hemicellulose or lignin.

Bleaching chemical wood pulp removes more of the lignin andhemicellulose.

In the manufacture of pulp woody material is disintegrated into fibersin a chemical pulping process. The fibers can then optionally bebleached. The fibers are then combined with water in a stock chest toform a slurry. The slurry then passes to a headbox and is then placed ona wire, dewatered and dried to form a pulp sheet. Additives may becombined with the fibers in the stock chest, the headbox or both.Materials may also be sprayed on the pulp sheet before, during or afterdewatering and drying. The kraft pulping process is typically used inthe manufacture of wood pulp.

There is a difference between wood fiber and wood pulp fiber. A woodfiber is a group of wood fibers held together by lignin. The lumens ofthe wood pulp fibers collapse during the drying process. The driedchemical wood pulp fibers are flat. The lumens of each of the woodfibers in the wood fiber bundle remain open. The flat wood pulp fibersare more flexible than wood fibers.

Cellulosic wood pulp fibers can be in the form of commercial cellulosicwood pulps. The pulp is typically delivered in roll or baled form. Thepulp sheet has two opposed substantially parallel faces and the distancebetween these faces will be the thickness of the particle. A typicalpulp sheet can be from 0.1 mm to 4 mm thick. In some embodiments thethickness may be from 0.5 mm to 4 mm.

The wood pulp sheet is formed into particles for the ease of meteringand combining with the thermoplastic polymer.

The fiber sheet, and the particles, can have a basis weight of from 12g/m² (gsm) to 2000 g/m². In one embodiment the particles could have abasis weight of 600 g/m² to 1900 g/m². In another embodiment theparticles could have a basis weight of 500 g/m² to 900 g/m². For a papersheet one embodiment could have a basis weight of 70 gsm to 120 gsm. Inanother embodiment a paperboard could have a basis weight of 100 gsm to350 gsm. In another embodiment a fiber sheet for specialty use couldhave a basis weight of 350 gsm to 500 gsm.

Pulp additives or pretreatment may also change the character of theparticle. A pulp that is treated with debonders will provide a looserparticle than a pulp that does not have debonders. A looser particle maydisperse more readily in the material with which it is being combined.The thickness of the pulp sheet is one factor that can determine thethickness of the particle.

In one embodiment the particle has a hexagonal shape, one embodiment ofwhich is shown in FIG. 1. The hexagon can be of any type from fullyequilateral to fully asymmetric. If it is not equilateral, the majoraxis may be from 4 to 8 millimeters (mm) and the minor axis may be from2 to 5 mm. Some of the sides of the hexagon may be of the same lengthand some or all of the sides may be of different lengths. Thecircumference or perimeter of the hexagon may be from 12 mm to 30 mm andthe area of the upper or lower face 24 or 26 of the particle may be from12 to 32 mm². In one embodiment the particles could have a thickness of0.1 to 1.5 mm, a length of 4.5 to 6.5 mm, a width of 3 to 4 mm and anarea on one face of 15 to 20 mm². In another embodiment the particlescould have a thickness of 1 to 4 mm, a length of 5 to 8 mm, a width of2.5 to 5 mm and an area on one face of 12 to 20 mm².

Two examples of a hexagonally shaped particle are shown.

In FIGS. 1-3, particle 10 is hexagon shaped and has two opposed sides 12and 18 which are equal in length and are longer than the other foursides 14, 16, 20 and 22. The other four sides 14, 16, 20 and 22 may bethe same length, as shown, or the four sides may be different lengths.Two of the sides, one at each end such as 14 and 20 or 14 and 22 may bethe same length, and the other two at each end, 16 and 22 or 16 and 20,may be the same length or have different lengths. In each of thesevariations, the sides 10 and 18 may the same length or of differentlengths. The edges of the particles may be sharp or rounded.

The distance between the top 24 and bottom 26 of particle 10 may be from0.1 mm to 4 mm.

FIGS. 4 and 5 illustrate an embodiment in which each of the six sidesthe hexagon is of a different length. The embodiment shown isillustrative and the order of the lengths of the sides and size of thelengths of the sides can vary.

Particles of the shape, size and basis weight described above can bemetered in weight loss and volumetric feeder systems well known in theart.

The alignment of the fibers within the particle can be parallel to themajor axis of the hexagon or perpendicular to the major axis of thehexagon or any orientation in between.

The hexagonal particles can be formed on a Henion dicer, but other meanscould be used to produce a hexagonal particle.

Other forms of pulp particles may also be used. The ease of addition maydepend on the shape of the particle.

The polymeric matrix functions as the host polymer and is a component ofthe melt processable composition including the chemical wood pulpfeedstock. Melt processing is used to combine the polymer and chemicalwood pulp fiber. In melt processing the polymer is heated and melted andthe chemical wood pulp fiber is combined with the polymer. During thisprocess the fibers are singulated.

The polymer is thermoplastic.

A wide variety of polymers conventionally recognized in the art assuitable for melt processing are useful as the polymeric matrix. Thepolymeric matrix substantially includes polymers that are sometimesreferred to as being difficult to melt process, especially when combinedwith an interfering element or another immiscible polymer. They includeboth hydrocarbon and non-hydrocarbon polymers. Examples of usefulpolymeric matrices include, but are not limited to high densitypolyethylene (HDPE), low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), polypropylene (PP)), polyolefin copolymers (e.g.,ethylene-butene, ethylene-octene, ethylene vinyl alcohol), polystyrene,polystyrene copolymers (e.g., high impact polystyrene, acrylonitrilebutadiene styrene copolymer), polyacrylates, polymethacrylates,polyesters, polyvinylchloride (PVC), fluoropolymers, Liquid CrystalPolymers, polyamides, polyether imides, polyphenylene sulfides,polysulfones, polyacetals, polycarbonates, polyphenylene oxides,polyurethanes, thermoplastic elastomers, epoxies, alkyds, melamines,phenolics, ureas, vinyl esters or combinations thereof. In certainembodiments, the most suitable polymeric matrices are polyolefins.

Polymeric matrices that are derived from recycled plastics are alsoapplicable as they are often lower cost. However, because such materialsare often derived from materials coming from multiple waste streams,they may have vastly different melt rheologies. This can make thematerial very problematic to process. The addition of cellulosicfeedstock to a recycled polymer matrix should increase the meltviscosity and reduce overall variability, thus improving processing.

In some embodiments the following thermoplastic polymers may be used:Biopolymers such as polylactic acid (PLA), cellulose acetate, cellulosepropionate, cellulose butyrate; polycarbonates, polyethyleneterephthalate, polyolefins such as polyethylene, high densitypolyethylene, low density polyethylene, linear low density polyethylene,polypropylene, polystyrene, polystyrene copolymers such asacrylonitrile-butadiene-styrene copolymer (ABS), styrene blockcopolymers, polyvinyl chloride (PVC), and recycled plastics.

The thermoplastic polymer may be selected from the group consisting ofbiopolymers, polylactic acid, cellulose acetate, cellulose propionate,cellulose butyrate; polycarbonates, polyethylene terephthalate,polyolefins, polyethylene, high density polyethylene, low densitypolyethylene, linear low density polyethylene, polypropylene,polystyrene, polystyrene copolymers, acrylonitrile-butadiene-styrenecopolymer, styrene block copolymers, polyvinyl chloride, and recycledplastics.

In one embodiment, the chemical wood pulp feedstock is melt processedwith an incompatible polymeric matrix (e.g., polyolefin). In anotherembodiment, the chemical wood pulp feedstock is melt processed with acompatible polymeric matrix (e.g., modified cellulosic polymers). Forexample, it has been found that when the chemical wood pulp feedstock ofthis invention is melt processed with cellulose propionate (Tenite™350E), the resulting composite has excellent fiber dispersion andmechanical properties.

The present invention also contemplates the use of compatibilizingagents in the composite formulation. Compatibilizing agents aretypically used to improve interfacial wetting of fillers with a polymermatrix. Addition of coupling agents or compatibilizers often improvesthe mechanical properties of the resulting composite material. Thepresent invention utilizes compatibilizing agents to improve wettingbetween the chemical wood pulp fiber of this invention and the polymermatrix as is known conventionally. However, we have also found thataddition of a compatiblizing agent improves dispersion of the chemicalwood pulp feedstock of this invention with some polymers.Compatibilizing agents and coupling agents are sometimes usedinterchangeably even though they perform differently to providecompatibility between the two materials.

Preferred compatibilizing agents for use with polyolefins arepolyolefin-graft-maleic anhydride copolymers. In one embodiment, thepolymer matrix and cellulosic feedstock is melt processed with apolyolefin-graft-maleic anhydride copolymer. Commercially availablecompatibilizing agents of this invention include those sold under thetradenames Polybond™ (Chemtura), Exxelor™ (Exxon Mobil), Fusabond™(DuPont), Lotader™ (Arkema), Bondyram™ (Maroon), Integrate (Equistar).The polymeric matrix may contain one or more fillers in addition to thechemical wood pulp feedstock. The polyolefin in the graft copolymer willbe the same as the polyolefin used as the polymer in the polymer matrix.For example polyethylene-graft-maleic anhydride would be used withpolyethylene and polypropylene-graft-maleic anhydride would be used withpolypropylene.

In one embodiment, amounts of about 5-10%, and in another 0.2-5% of thecompatibilizing agent is incorporated into composite formulations andmelt processable compositions.

Fillers and fibers other than chemical wood pulp fibers may be added tothe fiber/polymer blend to impart desirable physical characteristics orto reduce the amount of polymer needed for a given application. Fillersoften contain moisture and therefore reduce efficacy of a compatibilizerpresent in a polymeric matrix. Non-limiting examples of fillers andfibers include wood flour, natural fibers other than chemical wood pulpfiber, glass fiber, calcium carbonate, talc, silica, clay, magnesiumhydroxide, and aluminum trihydroxide.

In another aspect of the invention, the melt processable composition maycontain other additives. Non-limiting examples of conventional additivesinclude antioxidants, light stabilizers, fibers, blowing agents, foamingadditives, antiblocking agents, heat stabilizers, impact modifiers,biocides, flame retardants, plasticizers, tackifiers, colorants,processing aids, lubricants, compatibilizers, and pigments. Theadditives may be incorporated into the melt processable composition inthe form of powders, pellets, granules, or in any other extrudable orcompoundable form. The amount and type of conventional additives in themelt processable composition may vary depending upon the polymericmatrix and the desired physical properties of the finished composition.Those skilled in the art of melt processing are capable of selectingappropriate amounts and types of additives to match with a specificpolymeric matrix in order to achieve desired physical properties of thefinished material.

The composite polymers of this invention have wood pulp fibers uniformlydispersed within a thermoplastic polymeric matrix. The wood pulp fiberis first dispersed in a thermoplastic polymeric matrix in which woodpulp fiber is 65 to 90 weight % of the total composition.

There are problems associated with uniformly dispersing chemical woodpulp fibers throughout a polymer matrix. The fibers are initially in adried pulp sheet. The drying collapses the pulp fibers. The drying alsocauses the pulp fibers to bond together through hydrogen bonds. Thehydrogen bonds must be broken in order to obtain substantiallyindividual fibers. Some of the fibers will remain bonded. These arecalled knots or knits depending on the size. There will usually be a fewknots and knits remaining after breaking the hydrogen bonds betweenfibers.

There are also problems associated with providing the chemical wood pulpfiber at levels of 65 weight % or higher of the total weight of thefiber/polymer mix. The smaller amount of polymer means it is moredifficult to disperse the fiber in the polymer matrix. The fiber/polymermix becomes more viscous as the amount of fiber increases and it istherefore more difficult to move the fibers within the matrix to providedispersion. The purpose is to have very few fiber clumps

In one embodiment, the wood pulp feedstock of this invention is producedby mechanically dicing a wood pulp sheet material. In one embodiment,the wood pulp feedstock is diced into a hexagonal shape that isconducive for use with conventional feeding equipment. In otherembodiments the shapes may be triangular, rectangular or pentagon shapedparticles. The composites of this invention are produced by meltprocessing a polymeric matrix with chemical wood pulp feedstock. In oneembodiment, the chemical wood pulp feedstock is uniformly dispersedwithin the polymeric matrix after melt processing.

The present invention is directed at a solution to providing aneconomical means of producing composite materials which contain welldispersed chemical wood pulp fibers. This is achieved by utilizing awood pulp feedstock that has increased bulk density and is capable ofbeing fed into melt processing equipment using conventional feedingtechnology. The composites of this invention have wood pulp fibers welldispersed within a polymeric matrix.

The hydrogen bonded cellulose wood pulp fibers are then dispersed in thepolymer. One method is to make a master batch which is fiber rich having65 to 85 weight % of cellulose wood pulp fiber and 15 to 35 weight %polymer. Part of the polymer can be a compatibilizer if one is needed.

The initial addition of the cellulose pulp fiber to the polymer is a twostep operation.

In the first step the pulp particles are combined and mixed with thepolymer in a mixing operation. The mixing can occur in a thermokineticmixer or a Gelimat mixer,

The amount of chemical cellulose wood pulp fiber in the material is 65to 85 weight % and the amount of polymer is 15 to 35 weight %. If acompatibilizer is used then the amount of polymer will be reduced by theamount of compatibilizer. If 5 weight % compatilizer is used then theamount of polymer will be reduced by 5 weight %. Nonpolar polymer, suchas olefins, would use a compatibilizer. Typical compatibilizers aregraft copolymers such as maleic anhydride polypropylene or maleicanhydride polyethylene. If polypropylene is the polymer then up to 2weight % antioxidant will also be used. In one embodiment 0.5 wt %antioxidant would be used. The fiber and polymer will exit thethermokinetic mixer as a fluffy material.

A mixer 30 is shown in FIG. 6. The mixer 30 has a hopper 32 throughwhich the materials are fed. The materials are carried by a screw feeder34 into the mixing chamber 36 in which the blades 38 are rapidly rotatedby motor 40. The blades 38 rotate through the mix and the centrifugalforce created by the blades 38 moves the material outwardly against themixing chamber wall 42. The frictional heat melts the polymericmaterials, the polymer and the compatibilizer, and mixes the fiber withthe polymer. After mixing the polymer is removed from the mixing chamber36 through door 44.

Another method that can be used in the first step is a twin screwextruder with the die plate opened. The twin screw extruder has an opendie plate on the exit end so the flow of material from the extruder willnot be hindered. The amounts of fiber, polymer and compatibilizer is thesame as described above. The material will exit the twin screw extruderas a lumpy material. The twin screw mixer and its operation is describedin more detail below.

The problems to be solved are providing the fibers in a polymer matrixin a substantially individual form and metering the fibers into thepolymer in a substantially uniform amount so the wood pulpfiber/composite will have wood pulp fibers substantially uniformlydispersed throughout the composite. The present invention carries thediced particles of chemical wood pulp taken from the wood pulp sheet andmeters them into the polymer and substantially singulates the wood pulpfibers while mixing the wood pulp with the polymer.

In another embodiment, oil, such as mineral oil, may be added to thecomposite ingredients. In an embodiment the amount of mineral oil may befrom 0.1 to 5 weight % of the total weight of the materials in thecomposite polymer materials. In an embodiment the amount of mineral oilmay be from 0.1 to 2% of the total weight of the materials in thecomposite polymer materials. In an embodiment the amount of mineral oilmay be from 1 to 2% of the total weight of the materials in thecomposite polymer materials. In an embodiment the amount of mineral oilmay be from 1 to 1.5% of the total weight of the materials in thecomposite polymer materials. In an embodiment the amount of mineral oilmay be 1.15% of the total weight of the materials in the compositepolymer materials. The mineral oil increases the through-put of thecomposite through the extruders which may be used in the formation ofthe polymer and is believed to aid in the dispersion of the fibers inthe composite.

Mineral oil is a viscous oil having a specific gravity of from 0.8 to0.9. It can be clear, colorless and odorless. In an embodiment themineral oil is a standard white mineral oil. In an embodiment themineral oil is Drakol 600, CAS number 8042-47-5.

The mineral oil is added in the first master batch mixer and may beadded in subsequent mixers. It is added with the pulp particles and thethermoplastic polymer and aids in the mixing of the materials and thespeed of the process.

In FIG. 10, the bleached chemical wood pulp fiber particles 24 or 24 aenter twin screw extruder 100 through hopper 102. Polymer pellets alsoenter the twin screw extruder 100 through hopper 104. The hopper 104 maybe before or after hopper 102. The wood pulp fiber particles and thepolymer pellets may enter the twin screw extruder through the samehopper.

In one embodiment the twin screw extruder has an open die face. Inanother embodiment the twin screw extruder has a partially open die faceby using a restrictor 105. The partial opening 106 may be any shape. Inone embodiment the opening has an area that is 20 to 80% of the area ofthe open die face. In another embodiment is has an area that is 40 to60% of the total area of the open die face. The partial open die faceaids in the dispersion of the fibers in the polymer.

One embodiment of this die face is shown in FIG. 11. In this embodimentthe transition from the area of the die face to the area of the openingis gradual. The upper and lower faces 107 and 108 of the restrictor 105extend inwardly to constrict the flow of material toward the opening 106to provide an opening that has less height than the open die face andthe side faces 109 and 110 extend outwardly to provide an opening thatis wider than the open die face. The restrictor withstands the pressureof the material being pushed through the extruder and may be a singlemachined part.

Another embodiment is shown in FIG. 12. The opening is divided intoseveral openings 111. Again in one embodiment the opening has an areathat is 20 to 80% of the area of the open die face. In anotherembodiment is has an area that is 40 to 60% of the total area of theopen die face.

The amount of bleached chemical wood pulp fiber added to the polymer inthe twin screw extruder is 65 to 85 weight % of the total weight offiber, polymer and additives.

The first stage embodiments are the same for both the master batchcomposite in which 65 weight % to 85 weight % of the material is fiberand for the let-down composite in which 10 weight % to 50 weight % ofthe material is fiber.

The present invention is also directed to a solution to providing aneconomical means of producing composite polymeric materials whichinclude 10 to 50 weight percent chemical wood pulp fiber. In oneembodiment the pulp fibers are uniformly dispersed within the polymericmatrix.

In one embodiment the chemical wood pulp fiber is a bleached chemicalwood pulp fiber. There are reasons for using a bleached chemical woodpulp fiber instead of an unbleached wood pulp fiber.

One reason is color. A bleached chemical wood pulp fiber issubstantially all cellulose and hemicellulose. Cellulose andhemicellulose have no native color so they will impart little or nocolor to a composite. On the other hand, unbleached fibers such asnatural fibers like kenaf or whole wood fibers have up to 50% lignin andother compounds which can be colored in their native state or willbecome colored when heated to thermoplastic processing temperatures. Acomposite with unbleached, natural or whole wood fibers would becomecolored, probably a dark brown color.

Another reason is odor. Cellulose has no odor so a composite withbleached wood pulp fibers has very little odor contributed by thecellulose. Lignin and other components in unbleached fibers have strongcharacteristic odors when melt processed, imparting a strong odor to theresulting composite, limiting its use in enclosed areas such as theinterior of an automobile

An embodiment for a noncompatible polymer may contain the followingingredients:

Additive type Anti- Mineral Type Fiber Polymer Additives Compatibilizeroxidant Oil % fiber Wt % Wt. % Wt. % Wt. % Wt % Wt. % 85 85 7.2 7.8 5.70.6 1.5 70 70 23.6 6.4 4.7 0.5 1.2 65 65 29 6 4.4 0.5 1.1 55 55 40 5 3.70.4 0.9 50 50 45.4 4.6 3.4 0.4 0.9 46 46 49.8 4.2 3.1 0.3 0.8 45 45 50.94.1 3 0.3 0.8 40 40 56.3 3.7 2.7 0.3 0.7 36 36 60.7 3.3 2.4 0.3 0.6 3535 61.8 3.2 2.35 0.25 0.6 30 30 67.3 2.7 2 0.2 0.5 26 26 71.6 2.4 1.750.2 0.45 25 25 72.7 2.3 1.7 0.2 0.4 20 20 78.2 1.8 1.3 0.15 0.35 16 1682.5 1.5 1.1 0.1 0.3 15 15 83.6 1.4 1 0.1 0.3 10 10 89.1 0.90.7 >0.1 >0.2 6 6 93.45 0.55 0.4 >0.1 0.1

In the master batch the material will be further treated in a pelletmill, such as a California pellet mill, or a single screw extruder, suchas a Bonnot single screw extruder.

A laboratory version of a pellet mill is shown in FIGS. 7 and 8. Thepellet mill 50 has a hopper 52 into which the fiber/polymer compositematerial 54 from the thermokinetic mixer or twin screw extruder or othermixer is transferred. The composite material 54 falls onto perforatedplate 56. The apertures 58 on perforated plate 56 are the size of thediameter of the extruded pellets 60. A pair of wheels 62 forces thecomposite through the apertures 58 to form the pellets 60. The wheels 62are mounted on axels 64. The axels 64 are mounted on a rotor 66. Therotor 66 is rotated by a motor (not shown) to rotate the wheels 62around the perforated plate 56. The pellets 60 are removed from theapparatus and collected.

The tendency of the fibers at high fiber levels is to clump together. Inthe single screw extruder may be used to disperse the cellulose pulpfiber throughout the polymer. It was discovered that it was necessary todivert the flow of material through the extruder in order to obtaindispersion of the fiber. This is done by the placement of pins extendingfrom the outer wall of the extruder into the extruder cavity. Materialis forced from the apparatus through die holes to form extruded pellets.The material may have a tendency to block up behind the die plate andnot pass through the die in an efficient manner. The addition of a wiperat the back of the die face moves the composite material through the dieholes in a more efficient manner.

A single screw extruder is shown in FIG. 9. The extruder 80 has a hopper82 into which the fiber composite material from the mixer is placed. Thehopper 82 connects with a barrel 84 and a screw 86 extending through thebarrel 84. The screw 86 is rotated by a motor (not shown) and drives thematerial in the barrel toward the die plate 88. The design of the screwcan put more or less pressure on the composite as it travels through thebarrel. Pins 90 are placed along the barrel. The pins 90 may be movedinwardly or outwardly to divert the flow of material through the barreland aid in the dispersion of the fibers within the polymer The die plate86 has a number of apertures 92 through which the material passes toform strands which are optionally cut into pellets.

In one embodiment the first twin screw mixer may be connected directlyto the second single screw extruder and the material will pass directlyfrom the first mixer to the second. The same motor may operate both.This is shown in FIG. 14.

The master batch pellets contain 65 to 85 weight % chemical wood pulpfiber and 15 to 35 weight % polymer.

FIG. 10 is an embodiment of a process and apparatus for manufacturingthe polymeric composite having 50% or less chemical wood pulp fibers.

The material from the twin screw extruder is transferred to a secondtwin screw extruder 120 and additional polymer is added through hopper122. Other components may be added as well, either to the throat orthrough a side-stuffer (not shown in figure). The polymer is the same aswas used in the first twin screw extruder 100. The amount of polymeradded is the amount required to provide the desired wood pulp fiberloading in the composite.

In a batch operation the first twin screw extruder may be used as thesecond twin screw extruder by cycling the composite material through thefirst twin screw extruder a second time and adding the additionalpolymer in this second pass through the extruder. In this operation thedie face of the extruder would be changed from an open or partially opendie face to a die face having die openings to form extrudate.

The additional additives may also be added in the second twin screwextruder.

The composite is extruded through the die openings in the die plate andcut to size.

The extrudate from the second twin screw extruder may be formed intopellets by an underwater pelletizer. It has been thought that anunderwater pelletizer could not be used with pulp fiber because thefibers are hydrophilic. It has been found that an underwater pelletizercan be used and the moisture content of the fiber in the pellet is 1% orless. In some embodiments there is no deleterious effect due to waterpickup.

FIG. 15 is a diagram of an underwater pelletizer. The pellets exit thesecond twin screw extruder 120 through die apertures 124 in die plate126 into a cutting chamber 128 in which the extrudate is cut intopellets. The pellets are carried by water from the cutting chamber 128to a separation section 130 by pipe 132. The hot pellets are cooled bythe water. In one embodiment the pellets become spheroid shaped duringthe process. In the separation section 130 the pellets are separatedfrom the water by filtration. The separated water passes through a heatexchanger 134 in which the water is cooled. The water returns to cuttingchamber 128 through pipe 136.

The separated pellets pass through a dryer section 138 in which the restof the water is removed. A cyclone drier is shown but the drier can beany kind of drier. The dried pellets then pass into a pellet chute andinto a bagging operation in which the pellets are bagged.

There are a number of manufacturers of underwater pelletizers. Theseinclude Gala Industries, Neoplast, Berlyn and Davis Standard.

An underwater pelletizer has many advantages, but any type of pelletizermay be used.

A melt pump can be used to dampen the pressure and flow pulses generatedby the twin screw extruder, thus ensuring continuous and steady supplyof extrudate.

FIG. 14 shows another embodiment of the mixing system.

It may be necessary to obtain greater dispersion of the cellulose woodpulp fibers in the polymer. A mixing device such as the single screwextruder shown in FIG. 9 is placed between the two twin screw mixers.The single screw extruder is used to further disperse the fibers.

It should be understood that in the following discussion of thedifferent embodiments of the let-down pellet that any individual pelletmay have one or more of each of these embodiments.

In several of the following tests the composite polymer is molded into adogbone shape having the following dimensions: 6⅜ inches long, ⅛ inchthick, the end sections are ¾ inches wide, the central section is ½ inchwide and length of the central section is 2.7 inches or 68 mm. These arethe dimensions of a dogbone when it is mentioned in the text. Themolding of the dogbone is under heat and compression. Molding of amaster batch pellet with its large amount of fiber causes degradation ofthe fiber because of the large amount of heat and pressure required tomold the material causing the fiber to turn brown.

In an embodiment a let-down composite having 10 to 50 weight % bleachedchemical wood pulp fiber is provided. The remainder is polymer and otheradditives. In another embodiment a let-down composite is provided whichhas 20 to 40 weight percent bleached chemical wood pulp fibers and theremainder is polymer and other additives as noted above.

In an embodiment the let-down composite has a brightness of at least 20as measured by the Brightness Test. In another embodiment the let-downcomposite has a brightness of at least 30 as measured by the BrightnessTest.

The master batch composition, having 65 weight % or more fiber in thecomposition does not have this brightness because the heat and pressurerequired to form the material into a dogbone degrades the fiber andcauses a brown or black color.

Brightness Test

The method is that a light from a single source is focused and directedthrough an aperture onto the dogbone at an angle of 45 degrees and thereflected light passes through a filter having standard spectralcharacteristics and is then measured by a photodetector locatedperpendicular to the upper surface of the dogbone. The amount ofreflected light is compared with magnesium oxide, which has knownspectral characteristics which are stored in the instruments memory. Theratio of the reflected light to the magnesium oxide is expressed as apercentage.

The instrument is a Technidyne Brightimeter MICRO S-5. The instrumentshould be warmed up for 30 minutes prior to testing. The reflected lightpasses through a filter having an effective wave length of 457nanometers filter.

One dogbone is tested for each different condition of the composite suchas different polymer, different polymer amount, different fiber amount,different additives. There is a 1 kg. weight on top of the dogbone. Thedogbone is rotated through the four cardinal compass points, to givefour brightness values that are averaged.

In an embodiment or the let-down composite, the average dispersion ofbleached chemical wood pulp fibers in the let-down composite is equal toor greater than 90%. In another embodiment of the let-down composite theaverage dispersion of bleached chemical wood pulp fibers in the let-downcomposite is equal to or greater than 95%. In another embodiment theaverage dispersion of bleached chemical wood pulp fibers in the let-downcomposite is equal to or greater than 98%. In another embodiment theaverage dispersion of bleached chemical wood pulp fibers in the let-downcomposite is equal to or greater than 99%. Average dispersion means thefibers are substantially uniformly distributed throughout the compositeand the percentage is the number of fibers which are not in flocks.These percentages are determined using the Dispersion Test.

Dispersion Test

Measurement of dispersion is accomplished by using ImageJ (NIH). ImageJis freeware that can be downloaded athttp//imagej.nih.gov/ij/download.html. The Erode, Subtract Background,Analyze Particles and the other commands used in the custom macro beloware standard commands in ImageJ. The macro simply uses the standardIMageJ commands in a given order to obtain the information.

The samples are dogbones as described above. Xray photographs of thesamples are taken and the photographs are scanned to a digital image.The image is opened with ImageJ and the image is analyzed using thecustom macro.

The custom macro locates the samples in the image. It then performs theErode command four times to remove sample edge artifacts. It applies theSubtract Background command with a rolling ball diameter of 5 pixels, alight background and smoothing disabled. The grayscale image isconverted to black and white by using a threshold value supplied by theuser. A typical threshold value is 241.

The image now has black particles which correspond to undispersedfibers. The particles are counted using the Analyze Particles command.All particles except those touching the edge are counted. This isbecause there are often edge effects that look like a particle to themacro but are not actually a particle.

The other assumption is that the diced wood pulp material provided tothe process will divide or delaminate once along a center line and thesedivided particles may also divide or delaminate once along a centerline. The macro assumes that one-half of the analyzed particles willhave divided or delaminated once and the other half will have divided ordelaminated twice.

The macro reports the area of the undispersed particles. The macroassumes that one-half of the total area is occupied by once dividedundispersed particles and one-half of the total area is occupied bytwice divided particles.

The total weight of the undispersed particles or fibers is thencalculated. In the following discussion a pulp sheet having a basisweight of 750 grams per square meter (gsm) is used. The macro assumesthe basis weight of one-half of the particles, the once dividedparticles, have a basis weight of 375 gsm and the other half of theanalyzed particles, the twice divided particles, have a basis weight of187 gsm. The total weight of the undispersed particles or fibers isdetermined by the following formula:

Weight undispersed particles=0.0001*[0.5*(area of undispersedparticles)cm²*(375 gsm)+0.5*(area of undispersed particles)cm²*(187gsm)]

The weight percent of undispersed particles is found by the followingformula:

Weight % undispersed particles=100*Weight undispersed particles/Totalweight of fibers in sample

The weight percent of dispersed fibers is found by subtracting theweight percent of undispersed particles from 100 percent.

The actual macro is:

//HOW MANY SPECIMENS ARE IN THE IMAGE? N=10; //Now run the macrorun(“8-bit”); run(“Rotate 90 Degrees Right”); run(“Select All”);run(“Copy”); run(“Internal Clipboard”); setThreshold(0,200);run(“Convert to Mask”); k=1;//initialize k to 1 P=4;//number of Erodeoperations to perform    while (k<=P) { //this loop does multiple Erodes   run(“Erode”);    k=k+1;    } run(“Analyze Particles...”,“size=0-Infinity circularity=0.00-1.00 show=Nothing clear record add”);run(“Internal Clipboard”); run(“Subtract Background...”, “rolling=5light disable”); selectWindow(“Clipboard”); run(“Create Selection”);selectWindow(“Clipboard−1”); run(“Restore Selection”); //THE USER MUSTSET THE THRESHOLDING VALUE. 241 USUALLY WORKS WELL. setThreshold(0,241); run(“Convert to Mask”); run(“Make Binary”); k=0; M=N−1;//we countup from 0 not 1    while (k<=M) { //this loop does multiple AnalyzeParticles    roiManager(“Select”, k);    run(“Analyze Particles...”,“size=0-Infinity circularity=0.00-1.00    show=Nothing excludesummarize”);    k=k+1;    } close( ); close( );

Dispersion can depend on the amount of fiber loading. In an embodimentof the composite having 20 weight % bleached chemical wood pulp fiberthe dispersion was found to be equal to or greater than 99%. In anembodiment of the composite having 30 weight % bleached chemical woodpulp fiber the dispersion was found to be equal to or greater than 98%.In an embodiment of the composite having 40 weight % bleached chemicalwood pulp fiber the dispersion was found to be equal to or greater than92%.

The odor level of the let-down composite was compared to the odor levelsof the thermoplastic polymer which incorporated other materials. Threelevels of let-down composite were tested—polymer incorporating 20 weight% bleached chemical wood pulp fiber, incorporating 30 weight % bleachedchemical wood pulp fiber and incorporating 40 weight % bleached chemicalwood pulp fiber. These were compared to a control of the thermoplasticpolymer alone, with the polymer incorporating 30 weight % glass fiber,with the polymer incorporating 30 weight % sisal and with the polymerincorporating 30 weight % maple wood flour.

The test used was ASTM E679, using an Ac'scent olfactometer, availablefrom St. Croix Sensory, 1-800-879-9231. In this test the sample isplaced in a 9 L Tedlar bag at 40° C. for 24 hrs prior to testing. Theolfactometer uses a venture valve system where odor free air at highflow rate through the valve pulls air from the sample bag into the airstream. Dilution factors from 8 to 66,000 can be achieved. The reportednumber is the dilution factor at which sample odor was detected. Thehigher the dilution number the more odiferous is the material. Theresults are as follows:

Material Dilution to detection of odor Control 150 30% glass fiber 47030% sisal fiber 7200 30% maple wood flour 1500 20% bleached wood pulpfiber 350 30% bleached wood pulp fiber 300 40% bleached wood pulp fiber330

It can be seen that the dilution level of the thermoplastic polymer withbleached chemical wood pulp fiber is less than any of the othermaterials, including glass fiber, and is substantially the sameregardless of the amount of wood pulp fiber incorporated into thethermoplastic polymer.

In order to determine the usefulness of the let-down composite aMoldflow® report of the let-down pellets was commisioned. Moldflow®reports are used in the industry to determine how to cycle materialthrough a molding process, and to gain insight into the behavior of amaterial during the injection molding process. The report compared apolypropylene composite with 30% bleached chemical wood pulp fibers withtwo 20% glass filled polypropylene composites.

The following table from the report provides a cooling time study for aheavy duty part. The runners are the channel leading to the mold whichcan be run hot or cold. If cold then it has to be ejected with the part,trimmed off and recycled or discarded as waste. If hot, the contentsstay molten and are used as the first bit of injected plastic for thenext injection cycle.

Melt Cooling time to reach temperature ejection temperature Compositetype ° F. Runner Seconds 20% glass filled 380 Hot 136 polypropylene 380Cold 124 446 Hot 180 446 Cold 180 20% glass filled 380 Hot 126polypropylene 380 Cold 126 446 Hot 183 446 Cold 184 30% wood pulp fiber330 Hot 99 filled polypropylene 380 Cold 106 380 Hot 105 446 Cold 119

It can be see that the bleached chemical wood pulp fiber filledpolypropylene had a much shorter cooling time than the glass filledpolypropylene. This translates into faster cycle times and more partsproduced in a given period of time.

This is also shown in another table from the report which comparesgeneric “average” cycle times for molded parts for the 20% glass filledpolypropylene material and the 30% bleached chemical wood pulp fiberfilled polypropylene material.

20% glass filled 30% bleached chemical polypropylene wood pulp fiberfilled Process step material polypropylene material Filling time,seconds 3 3 Pack/Hold time, seconds 12 10 Cooling time, seconds 39 26Mold open/close, seconds 6 6 Total cycle time, seconds 60 45

The generic “average” cycle time for the material filled with chemicalwood pulp fibers is 75% of the cycle time for the glass filled material.This provides a much faster production rate.

It is also noted that the composition with 10 to 50 weight % wood pulpfiber and 25 to 85 weight % thermoplastic polymer has another attribute.The edges of molded structures are free or substantially free of tactiledefects. A tactile defect is a defect that can be felt when moving ahand or finger along the edge of the molded part. A tactile defectshould be distinguished from a visual defect. It is possible for a partto have a visual edge defect, one that can be seen, but not have atactile edge defect, one that can be felt. The edge of a part is theboundary layer between the two faces of the part. It is usually roundedor at an angle to the faces of the part. It is often rounded or at a 90°angle to the faces of the part. In one embodiment the edges would betactile defect free. In another embodiment the edge would average onetactile defect or less per foot or less of edge. In another embodimentthe edge would average two tactile defects or less per foot or less ofedge. The term “foot or less” means that if the total edge length isless than an exact number of feet then the total edge length will betreated as being the next largest foot length for the determination oftactile defects. For example if the structure has a total edge length of8 inches then it would be treated as having a total edge length of 1foot for determining the number of tactile defects, and if the totaledge length is 2 foot 4 inches then it would be treated as having atotal edge length of 3 feet in determining the number of tactiledefects.

The master batch pellet containing 65 to 85 weight percent fiber mayalso be let down to 10 to 50 weight percent fiber or 20 to 40 weightpercent fiber in the injection molding operation for forming moldedparts. The pellet is added to the injection molder and the additionalthermoplastic polymer needed to reduce the amount of fiber to 10 to 50weight percent fiber or 20 to 40 weight % fiber is added to theinjection molder. The polymer is let down to the final fiber amount andthe molded part is formed at the same time. This reduces the expense ofreducing the amount of fiber as a separate operation.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the claimed subject matter.

1. The method of making a pellet comprising wood pulp fiber andthermoplastic polymer, comprising extruding an extrudate comprising 10to 50 weight % wood pulp fiber and 45 to 85 weight % thermoplasticpolymer through a die, cutting a pellet from the extrudate, removing thepellet from the extrudate with water having a temperature less than theextrudate, filtering the pellet from the water wherein the wood pulpfiber in the pellet has a moisture content of 1% or less.
 2. The methodof claim 1 wherein the wood pulp fibers are bleached chemical wood pulpfibers.
 3. The method of claim 1 wherein the thermoplastic polymer isselected from the group consisting of biopolymers, polylactic acid,cellulose acetate, cellulose propionate, cellulose butyrate;polycarbonates, polyethylene terephthalate, polyolefins, polyethylene,high density polyethylene, low density polyethylene, linear low densitypolyethylene, polypropylene, polystyrene, polystyrene copolymers,acrylonitrile-butadiene-styrene copolymer, styrene block copolymers,polyvinyl chloride, and recycled plastics.
 4. The process of claim 1further comprising cooling the water filtered from the pellet, recyclingthe water to the extrudate.
 5. The method of claim 4 wherein the woodpulp fibers are bleached chemical wood pulp fibers.
 6. The method ofclaim 4 wherein the thermoplastic polymer is selected from the groupconsisting of biopolymers, polylactic acid, cellulose acetate, cellulosepropionate, cellulose butyrate; polycarbonates, polyethyleneterephthalate, polyolefins, polyethylene, high density polyethylene, lowdensity polyethylene, linear low density polyethylene, polypropylene,polystyrene, polystyrene copolymers, acrylonitrile-butadiene-styrenecopolymer, styrene block copolymers, polyvinyl chloride, and recycledplastics.
 7. The method of claim 1 further comprising pumping thematerial to the die.
 8. The method of claim 1 wherein extrudatecomprises 20 to 40 weight % wood pulp fiber and 55 to &5 weight %thermoplastic polymer.
 9. The method of claim 1 wherein the wood pulpfiber does not swell.
 10. The method of claim 9 wherein the wood pulpfibers are bleached chemical wood pulp fibers.
 11. The method of claim 9wherein the thermoplastic polymer is selected from the group consistingof biopolymers, polylactic acid, cellulose acetate, cellulosepropionate, cellulose butyrate; polycarbonates, polyethyleneterephthalate, polyolefins, polyethylene, high density polyethylene, lowdensity polyethylene, linear low density polyethylene, polypropylene,polystyrene, polystyrene copolymers, acrylonitrile-butadiene-styrenecopolymer, styrene block copolymers, polyvinyl chloride, and recycledplastics.
 12. The process of claim 9 further comprising cooling thewater filtered from the pellet, recycling the water to the extrudate.13. The method of claim 12 wherein the wood pulp fibers are bleachedchemical wood pulp fibers.
 14. The method of claim 12 wherein thethermoplastic polymer is selected from the group consisting ofbiopolymers, polylactic acid, cellulose acetate, cellulose propionate,cellulose butyrate; polycarbonates, polyethylene terephthalate,polyolefins, polyethylene, high density polyethylene, low densitypolyethylene, linear low density polyethylene, polypropylene,polystyrene, polystyrene copolymers, acrylonitrile-butadiene-styrenecopolymer, styrene block copolymers, polyvinyl chloride, and recycledplastics.
 15. The method of claim 9 further comprising pumping thematerial to the die.
 16. The method of claim 9 wherein extrudatecomprises 20 to 40 weight % wood pulp fiber and 55 to &5 weight %thermoplastic polymer.